Covid question...I have tried to get the answer from National health service but...no answer?

first of all, different countries have different sets of rules and regulations of international travel under the current COVID-19 pandemic.. the country of origin may not have specific rules about departure, but the country of destination WILL have plenty of rules and regulations on arrival.. so you may want to check their immigration website or make an inquiry at the nearest embassy/consulate of that destination country about their standards..

AFAIK, most countries around the world, only allow essential travel.. but different countries have different definitions of what essential travel is: some countries consider businessmen/women to be essential to their economies.. most countries would allow entry if you have a working visa at the destination country and/or family.. and most countries, would require a letter from a verified doctor before departure, and the compulsory 14 days quarantine on arrival at designated hotels - during this pandemic.. 

back to your question.. the RT-PCR (Nasal swab) test is the "gold" standard to test for COVID-19 virus (better known as SARS-CoV-2).. it is accurate and unfortunately expensive compared to the Antibody (blood) test for COVID-19 (which is not very reliable and dirt cheap - as cheap as a urine pregnancy test UPT).. only a lab technician could process the RT-PCR test, but any Tom, Dick and Harry, can operate the antibody (blood) test..

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the RT-PCR test detects the presence of the virus directly, while the antibody test detects the behaviour of our B-cells, and from the behaviour of the B-cells, we can deduce whether the virus is there or not.. it is the difference between seeing Peter with a new girlfriend at the party, or listening to your friend who may have seen Peter with a new girlfriend at the party, but not very sure..`

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in the past, a negative antibody test was a requirement for discharge from the hospital; this is NO longer the case; it is now more clinical (by observing signs & symptoms and other blood work-out..) to be discharged from the hospital.. and most countries will NOT accept antibody-test results without the RT-PCR test..

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the RT-PCR test detects the presence of the virus directly, while the antibody test only detects the level of readiness of our immune system (B-cells) against the COVID-19 virus (again better known as SARS-CoV-2).. if the RT-PCR test is positive, then almost 100% you have COVID-19, but if the RT-PCR test is negative, then there is a 97% chance that you do not have COVID-19..

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few people were tested positive on RT-PCR test but did not have COVID-19 and vice versa.. they were either recovering from COVID-19 as the last trace of the virus is dying (meaning they were not fully recovered from COVID-19) when the second RT-PCR test was made.. or they had COVID-19 for the second time.. and guess what; ONLY ONE CASE of a Japanese woman of which doctors believe that her case was a genuine second infection of COVID-19; while other similar cases was the extension of the first infection (the late shedding of COVID-19 virus from the first infection).. ONE CASE among millions of COVID-19 cases world-wide..!!

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what people fail to understand is that COVID-19 is a new disease; and we still learn new things about the virus, COVID-19 also attacks the brain, the kidneys and heart muscles; and it causes the loss of smell and hearing in people.. will we get a second infection of COVID-19 after getting the first one? we simply do not know.. the vast majority of people seem to be immune against COVID-19 after they were recovered from COVID-19 in the first time.. that one Japanese woman is the only exception on record against millions of COVID-19 cases world-wide..

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next the antibody test.. our adaptive immune system is divided into humoral and cellular immunity (or antibody-mediated immunity and cell-mediated immunity).. there were studies in the past (before COVID-19 pandemic) of which the latest French study by Strasbourg University Hospital (June 22nd) on COVID-19 cases has confirmed the previous assumptions.. this French study was conducted on families and people who had COVID-19 but tested negative on the blood antibody test..

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the French study tells us that the antibody test ONLY tests the activity of the antibody-mediated immunity by the B-cells while ignoring the other half, the cell-mediated immunity by the T-cells.. those families were tested negative on the antibody test until they were fully recovered.. fortunately, the people behind the French study tested the T-cell activity and they were tested positive (positive on the T-cells or cell-mediated test but negative on the antibody produced by the B-cell test), and unfortunately such test on cell-mediated immunity, is even MORE expensive than the RT-PCR test and the antibody test..   `furthermore, a KCL (King's collage London) study published in June 22nd; they found that COVID-19 antibodies dropped dramatically within weeks after the subjects were exposed to COVID-19 (SARS-Cov-2) virus.. as early as 12 weeks to projected 36 months.. 

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it is complicated, i know, and what i told you is just the tip of the ice-berg.. i am not an immunologist, but we've studied immunology in med-school and i remember students failing in exams on immunology.. most people and news media focus on the antibody-mediated immunity and forget/do not know about the other half, the cell-mediated immunity..

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when an infection comes, the B-cells grow in numbers and size to become Plasma Cells that are giant antibody factories going overtime to mass produce antibodies in high numbers.. but as the infection subsides, the Plasma cells shrink in numbers and size to produce less and less antibodies (it is expected).. however some of these B-cells do not grow to become Plasma Cells but instead they become dormant Memory B-cells that remembers the initial infection.. so on the next encounter with the same infection, these Memory B-cells are reactivated into Plasma Cells in a much faster rate with no or less/shorter symptoms of COVID-19 (from days down to hours and minutes)..

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similarly, some of the T-cells also become Memory T-cells instead of becoming large Cytotxic T-cells (aka. Killer T-Cells).. and these Memory B & T cells often stay dormant for years and decades, just waiting for the next encounter with the same infection.. and this is why when you read about potential vaccines for COVID-19, they would say that their vaccine produce good humoral and cellular response (both antibody-mediated and cell-mediated or both B-cells and T-cells immunity)..

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the main concern in the news right now, is about new strains of COVID-19.. the reason why we need to be vaccinated with the Flu vaccine every few months or years, because the Flu virus has several strains, influenzae A virus, influenzae B virus etc etc etc etc.. doctors choose the Flu vaccine according to the strain that is common in that area that year.. next year, could be a whole different strain of the virus that would require another injection.. 

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at the moment, new emerging strains of COVID-19 virus (SARS-CoV-2) produce less symptoms of COVID-19 (meaning they do not kill their victims) and they seem to respond very well to the current vaccines that are being studied.. which is why the news about COVID-19 vaccines often mention the term 'Cross-protection'..

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a flu vaccine offers some cross-protection against other strains of flu viruses.. but many existing vaccines have better cross-protection against Coronaviruses, which is why you may read about using the original SARS coronavirus (SARS-CoV-1) vaccine or using the MERS coronavirus (MERS-CoV) vaccine, or using Polio and TB vaccines; for COVID-19 (SARS-CoV-2) coronavirus vaccine research.. this Cross Protection is a feature of the T-cells cell-mediated immunity..

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the best estimates to have a safe vaccine for COVID-19, would be at the end of the year but most likely at the beginning of next year 2021.. the problem with the Russian COVID-19 vaccine, is the fact that it did NOT pass stage II nor stage III of human trials; which is like driving a car without seatbelts and pray that you would run into an accident.. but once a safe vaccine is available, we should see world travel restrictions less.. strict..

blood test on anti covid -antibodies have turned out to be remarkable, inconsistent. They are still making them, many are still using them, but they have had many issues with accuracy.