Dr. Anthony Fauci has testified before a Senate committee that he is worried that there may be a serious "Second Wave" oof the current SARS-CoV-2 pandemic in the United States. The basis for this fear is the experience over a century ago with the Spanish flu, still deadlier than the current pandemic. It came in three full waves, and of those the second was easily substantially larger than the other two. The lag between the first and second was several months, and as of now no nation that has had its first wave essentially ger under control has not had it under control for as long as that gap. So we are not yet in a position to see if this pandemic can or will imitate that former pandcmic.
Nevertheless, there is some evidence about the possibility of more immediate, less dramatic, second waves in the form of the number of new cases in a nation rising noticeably after having had a major decline from an initial peak. We have now seen this in a number of nations, in a small number quite dramatically. What is the current situation regarding this?
On May 11, the site endcoronavirus.org showed graphically the time path of new cases per day for 99 nations. This group divides these nations into three groups: "Winning" (32 nations) that have basically gotten their numbers well down, with a few exceptions; "Nearly There" (31 nations) that exhibit a variety of patterns, although nearly all currently below their peak by some; and "Need to Take Action" (36 nations), most of which simply are steadily moving up, although a small group have flattened (includes Moldova, Philippines, Poland, Romania, Sweden, and UK) or are slightly declining from a peak (including Ecuador, Finland, and US).
Out of each of these groups there are minorities that have exhibited seeing a noticeable upturn in the number of cases after noticeably declining from a peak, with some of those only showing a modest upturn, but a smaller group showing a substantial such upturn of moving back up at least halfway towards the previous peak, with a very small number actually moving back up above the previous peak. I shall note these particular set, but note that out of the 99 total, 16 have shown such a noticeable secondary increase, and out of those 7 that have exhibited a large such increase, with two of those moving back up beyond the previous peak. Who are these?
From the first group of nations, the ones supposedly "Winning" there are five that have moved up, with two of those having done so substantially. Those moving back up by small amounts are Croatia, Lithuania, and Vietnam, while those moving up a lot, both of them on the order of halfway back to the previous peak are Jordan and Lebanon (I am not sure why these last two are in this first group).
From the second group there are 7 that have shown some second uptick, with 3 of those more substantially so. Those first 4 are Bosnia, Costa Rica, Niger, and North Macedonia, while the 3 that have moved back substantially are Burkina Faso and Kyrgyzstan, both moving up about halfway, and San Marino, the natoin with the highest per capita rate of cases of all nations and that saw a decline of nearly half that was then followed by an increase that went above the first peak but has since been declining again.
Out of the final group, "Need to Take Action," there are 4 that have seen an increase after a peak, with two of those showing substantial secondary upticks. The first 2 are Iran and Singapore while the latter 2 are Azerbaijan, now back up to about half its former peak, and Iraq, which has moved back up itss former peak again.
Aa a broader perspective on all this I close by noting that a substantial portion of the world's 10 most populous nations are not only in the final group that need to take action, which included the US that is mildy declinging, they are simply rising solidly with little sign of flattening, with this group including Bangladesh, Brazil, India, Indonesia, Mexico, Nigeria, Pakistan, and Russia. Clearly this pandemic has a serious way to go, even if we luck out and avoid any really enormous second waves on the scale of the Spanish flu's one, which we have not yet seen out of any nations so far.
PS: I note that Germany, Lebanon, Singapore, and South Korea have all reimposed some previously lifted lockdown rules, even though the secondary outbreaks in two of these do not even show up in this data set (Germany and South Korea).