Back on August 3, the CDC issued new guidance regarding people who are infected with the coronavirus. It flew under the radar until the New Your Times wrote a story about that change. Following the NYT article, other media outlets improperly interpreted the new CDC guidance and wrote stories suggesting that immunity wanes after 3 months. That is not what the CDC guidance said.
What the CDC actually said was that “People who have tested positive for COVID-19 do not need to quarantine or get tested again for up to three months as long as they do not develop symptoms again. People who develop symptoms again within three months of their first bout of Covid-19 may need to be tested again if there is no other cause identified for their symptoms.”
Last Friday the CDC issued a clarifying statement saying, “Contrary to media reporting today… the latest data simply suggests that retesting someone in the 3 months following initial infection is not necessary unless that person is exhibiting the symptoms of COVID-19 and the symptoms cannot be associated with another illness.”
Some scientists have speculated that immunity from the virus might only last 3 months based on a study published in Nature back in June that showed many patients began to show decreasing levels of immunity 2–3 months after infection and that antibodies may not last very long among asymptomatic mildly ill persons.
But remember, antibodies are just one part of the immune system and it’s normal for antibodies to decrease once an infection recedes. It also doesn’t mean that waning antibody titers mean waning immunity. The memory B cells that first produced those antibodies are still around and stand ready to make more antibodies on demand. There is also good evidence that people infected with the SARS virus also generate a robust T-cell response- providing a longer lasting type of immunity.
Next week I’ll do a have a piece on the immune system and how it works with an eye toward the pandemic.