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2nd Covid vaccine several days before PCR tests, false positive risk?

Discussion in 'General Travel & Vacation Discussions' started by Kyle0692, May 3, 2021 at 9:54 PM.

  1. Kyle0692

    Kyle0692 Contributor

    # of Dives: 100 - 199
    Location: NE Florida
    Hey all!

    In about a month, my girlfriend and I are scheduled on our first liveaboard to the Turks and Caicos (Aggressor). I just got my first round of the Moderna Covid vaccine on April 28th and am due for the second shot on May 28th. Turks and Caicos requires a PCR test no more than 5 days before our flight, so I'd be looking at getting a couple tests that Wednesday (more than one just in case results take too long..) and I was just wondering if anyone had any thoughts/guidance on if getting the second vaccine several days beforehand would influence the test and make it more prone to be positive? I have looked online for an answer to this question and really can't find anything around this. If I had to, I would just wait a week to get the second round of vaccine until after my trip since we have already cancelled this trip once.


  2. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
    There is no virus -- dead or alive -- in the vaccine, so it should not affect the PCR test for the virus. Also, however, note that there is no harm caused by waiting an additional few weeks to get the second shot. It just delays your "fully vaccinated" status.
    divinh and Kyle0692 like this.
  3. living4experiences

    living4experiences ScubaBoard Sponsor ScubaBoard Sponsor

    # of Dives: 200 - 499
    Location: Tigard, Oregon
    I wouldn't worry so much about the influence on a COVID test but the possible side effects from the second dose. Most people that get side effects will have them after the second shot. Friends and family of mine have reported that the second dose knocked them for a loop for a full day and they took the day off of work. IMO, I wouldn't jeopardize a dive trip because of that. Best advice, though, would be to call your doctor. I've got a dive trip scheduled next week and my doctor advised to put off the vaccination until my return.
    divinh likes this.
  4. Centrals

    Centrals Barangay Pasaway

    # of Dives:
    Location: Hong Kong
    Could Vaccination Cause Me To Test Positive For Covid-19?

    Should had planned(if that was possible) the vaccination(2nd shot) at least 2 wks before travelling.
    The 2nd shot is a booster to enhance the protection offers by the first shot.
    There are suggestion for the 3rd shot in the future.

    Seek medical advice rather than coming here.
    divinh likes this.
  5. divinh

    divinh ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: San Francisco
    The vaccine causes your body to produce antibodies. A PCR test replicates any remnant of the virus in your nose and throat, but does not detect antibodies. The rapid Covid test looks for antibodies, which could show a false positive from a vaccine, however there is a supplemental test that can be done that will show that the antibodies are not from the virus. The supplemental test is routinely done for blood donations, when a person tests positive for antibodies.

    I donate blood. My first two donations after they started testing regularly, to look for plasma donors, showed negative for antibodies. After the vaccine, I tested positive for antibodies and the supplemental test showed it wasn't from Covid exposure.

    As for side effects, it can happen 12 hrs to 10 days later, from trials. It can happen even sooner or later. I, personally, got a slight arm rash after the first shot, seven days later. The second shot gave me chills and elevated temperature 12 hours later. Recovery is a couple of days.

    Given that you can take the vaccine later, it would be fine to delay, if you're worried about side effects during the trip, which others have pointed out.
  6. Centrals

    Centrals Barangay Pasaway

    # of Dives:
    Location: Hong Kong
    Unless you are using chinese produced vaccine(killed viral particle)!!! Impossible in USA but highly probable in many places including our own.

    Make sure you are well insured for the trip to cover any unlikely event.

    Postpone it by 2 wks to eliminate any lingering doubt/uncertainty.
  7. uncfnp

    uncfnp Solo Diver ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: North Carolina
    Hi Kyle and best wishes for a wonderful and safe trip!

    You have asked a very good question. Rest assured that the Moderna mRNA vaccine will not cause you to test positive on either a PCR test nor an antigen test. Both of these tests look for active desease. The PCR test detects viral RNA from an oral, or more often, a nasal swab. The mRNA vaccines use a very small segment of viral mRNA to “trick” the body in producing a bit of the viral spike protein. mRNA is very unstable and is broken down by the body within hours of vaccination. It will not produce covid RNA in the nose or throat and so can not result in a false positive PCR test.

    Anyone that tests positive for covid, PCR or antigen, after vaccination is considered to have an active infecion. If it is within 2 weeks the infection is considered to have occurred prior to the shot. If two weeks after vaccination is complete, it is considered a breakthrough infection.

    It is the same answer for covid antigen test. This test is for specific proteins on the surface of the virus in nasal/oral specimens. Neither the Pfizer nor Moderna vaccines will cause these proteins to be present so they can not cause a false positive covid test.

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